In image forming apparatuses, a photoreceptor drum serving as an image bearer, a development device, and the like are often housed in a common unit casing, thus forming a process cartridge (i.e., a modular unit) removably installed in the image forming apparatus.
In process cartridges, it is necessary to secure a gap between the photoreceptor drum and a development roller (i.e., a developer bearer) of the development device with a high degree of accuracy for good performance in image development. Accordingly, typically a rotary shaft of the development roller and that of the photoreceptor drum are held at both axial end positions by a side plate, serving as a planar connector, of the process cartridge to determine the distance between the development roller and the photoreceptor drum. To determine the position of the process cartridge relative to a body of the image forming apparatus, a positioning pin is provided to the planar connector, and a positioning hole in which the positioning pin fits is formed in the body of the image forming apparatus.
Additionally, a gear train is provided to the development device incorporated in the process cartridge for rotating the development roller and a developer conveyance member in predetermined directions at desired rotational frequencies, respectively. The gear train includes an idler gear rotatably attached to a shaft or rod projecting from a casing of the development device (hereinafter “development casing”).
In conventional process cartridges, when a relatively heavy load is applied to the development roller or the developer conveyance member, it is possible that the shaft rotatably supporting the idler gear is broken and falls down.
To prevent breakage of the shaft of the idler gear, a shaft insertion hole may be formed in the side plate of the process cartridge for supporting a tip of the shaft so that the shaft can be supported by both of the side plate of the process cartridge and the development casing. In this approach, however, a space dedicated for the shaft insertion hole must be secured at a specific position separately for insertion holes into which the rotary shafts of the development roller the photoreceptor drum are inserted, thereby determining the distance between them, or positioning holes for positioning of the process cartridge relative to the body of the image forming apparatus. This can impose a layout limitation, thus increasing the size of the side plate itself, the development device, and the entire process cartridge.